June 15, 2009
Expert Advises On The Do and Don’t Of Building In Hurricane-prone Areas
Better building practices for structures in hurricane-prone regions will be the focus of a paper next month in Caribbean Construction Magazine by NJIT architecture professor Rima Taher, PhD. Taher has written extensively about best building design and construction practices to reduce wind pressures on building surfaces and to resist high winds and hurricanes in residential or commercial construction.
She is a civil/structural engineer who teaches at NJIT's College of Architecture and Design. Her courses include topics related to wind and earthquakes with guidelines and recommendations for better design and construction in hurricane and earthquake prone areas. Taher also helps prepare architecture graduates for the certifying exam and has authored a book on the topic. In 2007, her article about the design of low-rise buildings for extreme wind events appeared in the Journal of Architectural Engineering.
"Certain home shapes and roof types can make a big difference," is a common refrain in all her work.
Her recommendations in the forthcoming article should be heeded by anyone building in high wind regions. They include the following.
Design buildings with square, hexagonal or even octagonal floor plans with roofs of multiple slopes such as a four-sloped hip roof. These roofs perform better under wind forces than the gable roofs with two slopes. Gable roofs are common only because they are cheaper to build. Research and testing demonstrate that a 30-degree roof slope will have the best results.
Wind forces on a roof tend to uplift it. "This explains why roofs blow off during extreme wind events," Taher said. To combat uplift, she advises connecting roofs to walls strongly with nails, not staples. Stapled roofs were banned in Florida after Hurricane Andrew. The use of hurricane clips is recommended. The choice of roofing is important. Different roofing systems perform differently under hurricane conditions. In tile roofs, loose tiles often become wind-borne debris threatening other structures.
Aim for strong connections between the structure and foundation. Structural failure-- one structural element triggering the collapse of another"”can be progressive.
Hurricane shutters can protect glazing from wind-borne debris. Various designs are available.
Roof overhangs are subject to wind uplift forces which could trigger a roof failure. In the design of the hurricane-resistant home, the length of these overhangs should be limited to about 20 inches.
The design of the researched cyclonic home includes simple systems to reduce the local wind stresses at the roof's lower edges such as a notched frieze or a horizontal grid. Install the latter at the level of the gutters along the homes' perimeter.
An elevated structure on an open foundation reduces the risk of damage from flooding and storm-driven water. All foundation piles must be strengthened by bracing and should penetrate deep enough into the soil to reduce the risk of scour.
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